The growing participation by women in the workforce and physical fitness has mandated a focused study of exercise during pregnancy. Currently, the scientific literature is limited in delineating clear and specific exercise guidelines for promoting maternal health while minimizing fetal risk. The existing exercise guidelines for pregnant women are equivocal at best and perhaps without scientific basis. The focus of the proposed program is to examine maternal and fetal hemodynamic repercussions of medically accepted levels of acute, non- weight-bearing exercise. The primary objective of this three-year program is to advance the candidate's knowledge and research skills in the area of exercise and pregnancy, by intensive training and extensive mentorship. The major aims of the proposed study are: 1) To assess longitudinally the maternal-fetal hemodynamic repercussions during exercise; 2) to define the relationships among exercise intensity, uterine artery blood flow change, and umbilical artery blood flow change, while monitoring fetal safety; and 3) to assess the safety limits of exercise throughout gestation, according to the indices of maternal heart rate and Rating of Perceived Exertion. This experimental study will employ a repeated-measures design with a sample of healthy, non-smoking, pregnant volunteers (n=45). Maternal heart rate, RPE, cardiac output, stroke volume, arterial pressure, uterine artery blood flow, and umbilical artery blood flow will be measured at different gestation periods and exercise intensities. The exercise tests will be conducted with a discontinuous, symptom-limited protocol. The study will ultimately aide development of unequivocal exercise guidelines for healthy pregnant women, while strengthening the candidate's career in this area.